Tripping Network Protectors to Protect Service Entrance Conductors to Industrial and Commercial Buildings

A most vital part of the electric system in large commercial and industrial buildings is the service entrance. Unfortunately it is located in a "no-man's land" between the electric power company's system and the low-voltage system. Much better understanding of the disadvantages and danger in providing a single 6000-18 000-ampere service entrance into a building is needed by electric power company engineers, low-voltage system consultants, and code-making authorities. Some codes and authorities are still insisting on a single service entrance into a building with little consideration of the possibility of loss of power to the entire building due to an arcing burndown or of the problem of high operating temperatures in these special high-current services. This paper shows how, in one case, arcing protection for the service entrance busway and switchboard was provided by using a groundfault relay to trip four network protectors. Six recommendations are made for improving the safety and reliability of future service entrances.